A Novel Current Self-Balancing Method for High-Gain and High-Frequency Converter

Abstract

Matrix transformer is deemed the most widely used structure for large current application due to its natural current sharing. However, multiple transformers suffer from large core volume and core loss, especially with high frequency operation. In this paper, a novel current self-balancing method for high-gain and high-frequency converter is proposed. Only one magnetic core is employed and all secondary windings for large current are wrapped parallelly around the core. The H-bridges with two filtering inductors on the DC positive and negative bus are cascaded by these secondary windings to form a proposed cascaded H-bridge structure. Due to the large impedance in filter inductor loop in high frequency, the differential-mode current between different windings is largely suppressed and the current sharing of secondary windings and SR MOSFETs is achieved naturally. The filtering inductor can be easily implemented by using PCB-routed inductance without iron core, which means that the power density and efficiency will not be impaired. A 750V/48V-2kW unregulated LLC converter prototype is built and achieves the power density of 7 kW/L with maximum efficiency of 96.5%. With the proposed cascaded H-bridge structure, current self-balancing is achieved perfectly and the efficiency improvement reaches to 0.8% at full loading condition.